Hyperplastic disorders of the skin including the Proteus syndrome (PS) and the Klippel-Trenaunay Weber (KTWS) syndrome are an important class of genetic disease. These disorders comprise a class of diseases that are due to somatic mutations in genes that are found only in the mosaic state, are not heritable, and therefore can not be evaluated by linkage analysis. We have begun to analyze patients with the Proteus Syndrome using comparative genome hybridization and genotype analysis to search for evidence of mosaic, segmental chromosome copy number alterations or uniparental disomy in sporadic mosaic disorders of the skin. The approach will be to compare hyperplastic and normal tissue from persons affected with PS or KTWS and to compare these results to those of the parents. We have acquired specimens from two remarkable patients with these disorders including a pair of identical twins who are discordant for Proteus syndrome and an unfortunate individual who recently underwent a below the knee amputation due to complications from Proteus syndrome. Preliminary examinations of these specimens by microsatellite screening show no alterations in the hyperplastic tissue.